Numerical models based on finite-difference or finite-element methods are used by various research groups in studies of radon-222 transport through soil and building materials. Applications range from design of radon remediation systems to morefundamental studies of radon transport. To ascertain that results obtained with these models are of good quality, it is necessary that such models are tested. This document reports on a benchmark test organized by the EU project ERRICCA: European Researchinto Radon in Construction Concerted Action. The test comprises the following cases: (1) Steady-state diffusive radon profiles in dry and wet soils, (2) steady-state entry of soil gas and radon into a house, (3) time-dependent radon exhalation from abuilding-material sample. These cases cover features such as: soil heterogeneity, anisotropy, 3D-effects, time dependency, combined advective and diffusive transport of radon, flux calculations, and partitioning of radon between air and water in soilpores. Seven groups participated in the intercomparison. All groups submitted results without knowing the results of others. For these results, relatively large group-to-group discrepancies were observed. Because of this, all groups scrutinized theircomputations (once more) and engaged in follow-up discussions with others. During this debugging process, problems were indeed identified and eliminated. The accordingly revised results were in better agreement than those reported initially. Somediscrepancies, however, still remain. All in all, it seems that the exercise has served its purpose and stimulated improvements relating to the quality of numerical modelling of radon transport. To maintain a high quality of modelling, it is recommendedthat additional exercises are carried out.